scholarly journals Implications of Einstein–Maxwell dilaton–axion gravity from the black hole continuum spectrum

2020 ◽  
Vol 500 (1) ◽  
pp. 481-492
Author(s):  
Indrani Banerjee ◽  
Bhaswati Mandal ◽  
Soumitra SenGupta
Keyword(s):  
Black Hole ◽  
High Energy ◽  
Accretion Disc ◽  
Optical Observations ◽  
Optical Data ◽  
Inflationary Cosmology ◽  
Theoretical Spectrum ◽  
Late Time ◽  
Heterotic String Theory ◽  
Continuum Spectrum

ABSTRACT String inspired models can serve as potential candidates to replace general relativity (GR) in the high-energy/high-curvature regime where quantum gravity is expected to play a vital role. Such models not only subsume the ultraviolet nature of gravity but also exhibit promising prospects in resolving issues like dark matter and dark energy, which cannot be adequately addressed within the framework of GR. The Einstein–Maxwell dilaton–axion (EMDA) theory that is central to this work is one such string inspired model arising in the low energy effective action of the heterotic string theory with interesting implications in inflationary cosmology and in the late-time acceleration of the Universe. It is therefore important to survey the role of such a theory in explaining astrophysical observations, e.g. the continuum spectrum of black holes which is expected to hold a wealth of information regarding the background metric. The Kerr–Sen space–time corresponds to the exact, stationary, and axisymmetric black hole solution in EMDA gravity, possessing dilatonic charge and angular momentum originating from the axionic field. In this work, we compute the theoretical spectrum from the accretion disc around quasars in the Kerr–Sen background assuming the thin accretion disc model due to Novikov and Thorne. This is then used to evaluate the theoretical estimates of optical luminosity for a sample of eighty Palomar Green quasars which are subsequently compared with the available observations. Our results based on χ2 analysis indicate that the dilaton parameter r2 ∼ 0.2 is favoured by optical observations of quasars which is further corroborated by other error estimators e.g. the Nash–Sutcliffe efficiency, the index of agreement and their modified versions. We further report that strong dilaton charges (r2 > 1.6) are disfavoured by quasar optical data and the spins associated with the quasars are also estimated.

scholarly journals The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR

2020 ◽  
Vol 494 (4) ◽  
pp. 6012-6029 ◽  
Author(s):  
D J Walton ◽  
C Pinto ◽  
M Nowak ◽  
M Bachetti ◽  
R Sathyaprakash ◽  
...  
Keyword(s):  
Black Hole ◽  
Broad Band ◽  
High Energy ◽  
Accretion Disc ◽  
Continuum Emission ◽  
Spectral Variability ◽  
Temperature Behaviour ◽  
Temperature Relation ◽  
X Ray ◽  
Constant Area

ABSTRACT We present results from the major coordinated X-ray observing programme on the ULX NGC 1313 X-1 performed in 2017, combining XMM–Newton, Chandra, and NuSTAR, focusing on the evolution of the broad-band (∼0.3–30.0 keV) continuum emission. Clear and unusual spectral variability is observed, but this is markedly suppressed above ∼10–15 keV, qualitatively similar to the ULX Holmberg IX X-1. We model the multi-epoch data with two-component accretion disc models designed to approximate super-Eddington accretion, allowing for both a black hole and a neutron star accretor. With regards to the hotter disc component, the data trace out two distinct tracks in the luminosity–temperature plane, with larger emitting radii and lower temperatures seen at higher observed fluxes. Despite this apparent anticorrelation, each of these tracks individually shows a positive luminosity–temperature relation. Both are broadly consistent with L ∝ T4, as expected for blackbody emission with a constant area, and also with L ∝ T2, as may be expected for an advection-dominated disc around a black hole. We consider a variety of possibilities for this unusual behaviour. Scenarios in which the innermost flow is suddenly blocked from view by outer regions of the super-Eddington disc/wind can explain the luminosity–temperature behaviour, but are difficult to reconcile with the lack of strong variability at higher energies, assuming this emission arises from the most compact regions. Instead, we may be seeing evidence for further radial stratification of the accretion flow than is included in the simple models considered, with a combination of winds and advection resulting in the suppressed high-energy variability.

scholarly journals X-rays from Photoionized Accretion Discs

1994 ◽  
Vol 159 ◽  
pp. 380-380
Author(s):  
G. Matt ◽  
A.C. Fabian ◽  
R.R. Ross
Keyword(s):  
Black Hole ◽  
Seyfert Galaxies ◽  
High Energy ◽  
Accretion Disc ◽  
Accretion Discs ◽  
X Rays ◽  
Central Black Hole ◽  
X Ray

The presence of iron lines and high energy excesses in the X-ray spectra of Seyfert galaxies has been firmly established by Ginga (e.g. Nandra & Pounds 1993 and references therein). These features are generally interpreted as signatures of the reprocessing of the primary X-rays by matter in the neighbourhood of the central black hole, probably distributed in an accretion disc (Lightman & White 1988, George & Fabian 1991, Matt, Perola & Piro 1991).

scholarly journals GRS 1915+105 “celebrates its majority” (1992–2010)

2010 ◽  
Vol 6 (S275) ◽  
pp. 270-274
Author(s):  
Alberto J. Castro-Tirado
Keyword(s):  
Black Hole ◽  
Radio Galaxies ◽  
High Energy ◽  
Accretion Disc ◽  
Γ Ray ◽  
High Energy Particles ◽  
Travel Distances ◽  
Open Issues

AbstractOver the 18 years since its discovery, GRS 1915+105 has continuously brightened in the X/γ-ray sky. It is considered the prototypical microquasar. Most of these are LMXBs that show sporadic ejection of matter at apparently superluminal velocities. In these the three basic ingredients of quasars are found: a black hole, an accretion disc and collimated jets of high energy particles, but in microquasars the black hole is only a few M⊙ instead of several × 106 M⊙; the accretion disc had mean thermal temperature of several × 106 K instead of several × 103 K, and the particles ejected at relativistic speeds travel distances of a few ly only, compared to few × 106 ly as in radio galaxies. However many open issues remain to be addressed.

scholarly journals High Energy Gamma Rays from Accretion Disc

1981 ◽  
Vol 94 ◽  
pp. 335-336
Author(s):  
F. Giovannelli ◽  
S. Karakula ◽  
W. Tkaczyk
Keyword(s):  
Black Hole ◽  
Gamma Rays ◽  
Gamma Quantum ◽  
High Energy ◽  
Accretion Disc ◽  
Inelastic Collisions ◽  
Production Spectrum ◽  
Hot Plasma ◽  
Energy Gamma ◽  
Γ Rays

In the case of spherical symmetric accretion into a black hole, the matter may be heated up to the temperature KT = 0.1 mpc2 (Kolykhalov and Sunyaev, 1979). In such a hot plasma inelastic collisions of protons may produce Π° which is the gamma quantum source.In this work we determined γ-rays production spectrum in the comoving plasma reference frame, expected γ-rays spectrum for the case of spherica symmetric accretion of matter into a black hole and the upper limit to the number of black holes in Galaxy is evaluated.

scholarly journals Living on the edge: Rossby wave instability and HFQPOs in black hole binaries

2020 ◽  
Vol 638 ◽  
pp. A33 ◽  
Author(s):  
P. Varniere ◽  
F. H. Vincent ◽  
F. Casse
Keyword(s):  
Black Hole ◽  
Rossby Wave ◽  
Kerr Black Hole ◽  
High Energy ◽  
Accretion Disc ◽  
Wave Instability ◽  
Stable Orbit ◽  
X Ray ◽  
General Relativistic ◽  
The Impact

Context. The Rossby wave instability (RWI) has been proposed to explain the origin of the high-frequency quasi-periodic oscillations observed in the X-ray emission of astrophysical systems harbouring black holes. Recent numerical computations have proven that the RWI does exist in a general relativistic context and that its presence is associated with a time-variable X-ray emission from the disc. Aims. Using our new Numerical Observatory of Violent Accreting system, NOVAs, we explore the way the RWI impacts an accretion disc orbiting a spinning black hole under realistic astrophysical conditions. Our aim is to study the impact of the presence of the RWI in the very inner part of the accretion disc on known observables and explore some possibly new ones. Methods. We present the first full general relativistic hydrodynamical simulations of the RWI occurring at the last stable orbit of an accretion disc orbiting around a Kerr black-hole. Those simulations, coupled with a full general relativistic ray-tracing, have allowed us to directly compare our simulations with the observables we obtained from the X-ray emission of the disc. Results. Our study shows, for the first time, that the RWI naturally arises near the inner edge of an accretion disc whenever it gets close to its last stable orbit, as predicted analytically. From there, we show that not only does the RWI create a visible timing feature but it also impacts the energy spectrum of the source, which exhibits a high energy extension due to the presence of hot vortices generated by the RWI in the disc. Our study also shows that systems with the RWI present at the inner edge of the disc only exhibit similar behavior to systems in which HFQPOs have been detected.

scholarly journals Accretion disc by Roche lobe overflow in the supergiant fast X-ray transient IGR J08408−4503

2019 ◽  
Vol 631 ◽  
pp. A135 ◽  
Author(s):  
L. Ducci ◽  
P. Romano ◽  
L. Ji ◽  
A. Santangelo
Keyword(s):  
Binary Systems ◽  
Dynamic Range ◽  
Compact Object ◽  
Accretion Disc ◽  
Roche Lobe ◽  
Optical Observations ◽  
Optical Data ◽  
X Ray ◽  
Orbital Parameters ◽  
Large Size

Supergiant fast X-ray transients (SFXTs) are X-ray binary systems with a supergiant companion and likely a neutron star, which show a fast (∼103 s) and high variability with a dynamic range up to 105−6. Given their extreme properties, they are considered among the most valuable laboratories to test accretion models. Recently, the orbital parameters of a member of this class, IGR J08408−4503, were obtained from optical observations. We used this information, together with X-ray observations from previous publications and new results from X-ray and optical data collected by INTEGRAL and presented in this work, to study the accretion mechanisms at work in IGR J08408−4503. We found that the high eccentricity of the compact object orbit and the large size of the donor star imply Roche lobe overflow (RLO) around the periastron. It is also likely that a fraction of the outer layers of the photosphere of the donor star are lost from the Lagrangian point L2 during the periastron passages. On the basis of these findings, we discuss the flaring variability of IGR J08408−4503 assuming the presence of an accretion disc. We point out that IGR J08408−4503 may not be the only SFXT with an accretion disc fueled by RLO. These findings open a new scenario for accretion mechanisms in SFXTs, since most of them have so far been based on the assumption of spherically symmetric accretion.

HIGH ENERGY PROCESSES IN THE VICINITY OF THE KERR'S BLACK HOLE HORIZON

2011 ◽  
Vol 03 ◽  
pp. 342-353 ◽  
Author(s):  
A. A. GRIB ◽  
YU. V. PAVLOV ◽  
O. F. PIATTELLA
Keyword(s):  
Black Hole ◽  
Relative Velocity ◽  
Lorentz Factor ◽  
High Energy ◽  
Accretion Disc ◽  
Centre Of Mass ◽  
Particle Collisions ◽  
Multiple Collision ◽  
The Earth ◽  
Energy Processes

Two particle collisions close to the horizon of the rotating nonextremal black hole are analyzed. It is shown that high energy of the order of the Grand Unification scale in the centre of mass of colliding particles can be obtained when there is a multiple collision – the particle from the accretion disc gets the critical momentum in first collision with the other particle close to the horizon and then there is a second collision of the critical particle with the ordinary one. High energy occurs due to a great relative velocity of two particles and a large Lorentz factor. The dependence of the relative velocity on the distance to horizon is analyzed, the time of movement from the point in the accretion disc to the point of scattering with large energy as well as the time of back movement to the Earth are calculated. It is shown that they have reasonable order.

scholarly journals HIGH ENERGY PROCESSES IN THE VICINITY OF THE KERR'S BLACK HOLE HORIZON

2011 ◽  
Vol 26 (22) ◽  
pp. 3856-3867 ◽  
Author(s):  
A. A. GRIB ◽  
YU. V. PAVLOV ◽  
O. F. PIATTELLA
Keyword(s):  
Black Hole ◽  
Relative Velocity ◽  
Lorentz Factor ◽  
High Energy ◽  
Accretion Disc ◽  
Centre Of Mass ◽  
Particle Collisions ◽  
Multiple Collision ◽  
The Earth ◽  
Energy Processes

Two particle collisions close to the horizon of the rotating nonextremal black hole are analyzed. It is shown that high energy of the order of the Grand Unification scale in the centre of mass of colliding particles can be obtained when there is a multiple collision – the particle from the accretion disc gets the critical momentum in first collision with the other particle close to the horizon and then there is a second collision of the critical particle with the ordinary one. High energy occurs due to a great relative velocity of two particles and a large Lorentz factor. The dependence of the relative velocity on the distance to horizon is analyzed, the time of movement from the point in the accretion disc to the point of scattering with large energy as well as the time of back movement to the Earth are calculated. It is shown that they have reasonable order.

scholarly journals X-Ray Determination of the Black-Hole Mass in Cygnus X-1

1998 ◽  
Vol 188 ◽  
pp. 388-389
Author(s):  
A. Kubota ◽  
K. Makishima ◽  
T. Dotani ◽  
H. Inoue ◽  
K. Mitsuda ◽  
...  
Keyword(s):  
Black Hole ◽  
Compact Object ◽  
Optical Observations ◽  
Black Hole Mass ◽  
X Ray ◽  
Upper Limit ◽  
Supergiant Star ◽  
X Ray Binaries ◽  
Two Bodies

About 10 X-ray binaries in our Galaxy and LMC/SMC are considered to contain black hole candidates (BHCs). Among these objects, Cyg X-1 was identified as the first BHC, and it has led BHCs for more than 25 years(Oda 1977, Liang and Nolan 1984). It is a binary system composed of normal blue supergiant star and the X-ray emitting compact object. The orbital kinematics derived from optical observations indicates that the compact object is heavier than ~ 4.8 M⊙ (Herrero 1995), which well exceeds the upper limit mass for a neutron star(Kalogora 1996), where we assume the system consists of only two bodies. This has been the basis for BHC of Cyg X-1.

scholarly journals Nanoscale optical writing through upconversion resonance energy transfer

2021 ◽  
Vol 7 (9) ◽  
pp. eabe2209
Author(s):  
S. Lamon ◽  
Y. Wu ◽  
Q. Zhang ◽  
X. Liu ◽  
M. Gu
Keyword(s):  
Graphene Oxide ◽  
Energy Transfer ◽  
Energy Consumption ◽  
Data Storage ◽  
High Capacity ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
High Energy ◽  
Optical Data ◽  
Upconversion Nanoparticles

Nanoscale optical writing using far-field super-resolution methods provides an unprecedented approach for high-capacity data storage. However, current nanoscale optical writing methods typically rely on photoinitiation and photoinhibition with high beam intensity, high energy consumption, and short device life span. We demonstrate a simple and broadly applicable method based on resonance energy transfer from lanthanide-doped upconversion nanoparticles to graphene oxide for nanoscale optical writing. The transfer of high-energy quanta from upconversion nanoparticles induces a localized chemical reduction in graphene oxide flakes for optical writing, with a lateral feature size of ~50 nm (1/20th of the wavelength) under an inhibition intensity of 11.25 MW cm−2. Upconversion resonance energy transfer may enable next-generation optical data storage with high capacity and low energy consumption, while offering a powerful tool for energy-efficient nanofabrication of flexible electronic devices.

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